function plus(){
    var num1 = document.getElementById("num1").value;
    var num2 = document.getElementById("num2").value;
    var result = parseInt(num1)+parseInt(num2);
    document.getElementById("result").value=result;
}
function jianfa(){
    var num1 = document.getElementById("num1").value;
    var num2 = document.getElementById("num2").value;
    var result = parseInt(num1)-parseInt(num2);
    document.getElementById("result").value=result;
}
function chengfa(){
    var num1 = document.getElementById("num1").value;
    var num2 = document.getElementById("num2").value;
    var result = parseInt(num1)*parseInt(num2);
    document.getElementById("result").value=result;
}
function chufa(){
    var num1 = document.getElementById("num1").value;
    var num2 = document.getElementById("num2").value;
    var result = parseInt(num1)/parseInt(num2);
    document.getElementById("result").value=result;
}